It is well known that anomalies in the shape of the eye can be the cause of visual disorders. Normal vision occurs when light that passes through and is refracted by the cornea, the lens, and other portions of the eye, and converges at or near the retina. Myopia or near-sightedness occurs when the light converges at a point before it reaches the retina and, conversely, hyperopia or farsightedness occurs when the light converges a point beyond the retina. Other abnormal conditions include astigmatism where the outer surface of the cornea is irregular in shape and effects the ability of light to be refracted by the cornea. In addition, in patients who are older, a condition called presbyopia occurs in which there is a diminished power of accommodation of the natural lens resulting from the loss of elasticity of the lens, typically becoming significant after the age of 45.
Corrections for these conditions through the use of implants within the body of the cornea have been suggested. Various designs for such implants include solid and split-ring shaped, circular flexible body members and other types of ring-shaped devices that are adjustable. These implants are inserted within the body of the cornea for changing the shape of the cornea, thereby altering the its refractive power.
These types of prostheses typically are implanted by first making a tunnel and/or pocket within the cornea which leaves the Bowman's membrane intact and hence does not relieve the inherent natural tension of the membrane.
In the case of hyperopia, the corneal curvature must be steepened, and in the correction of myopia, it must be flattened. The correction of astigmatism can be done by flattening or steepening various portions of the cornea to correct the irregular shape of the outer surface. Bi-focal implants can be used to correct for presbyopia.
It has been recognized that desirable materials for these types of prostheses include various types of hydrogels. Hydrogels are considered desirable because they are hydrophilic in nature and have the ability to transmitting fluid through the material. It has been accepted that this transmission of fluid also operates to transmit nutrients from the distal surface of the implant to the proximal surface for providing proper nourishment to the tissue in the outer portion of the cornea.
However, while hydrogel lenses do operate to provide fluid transfer through the materials, it has been found that nutrient transfer is problematic because of the nature of fluid transfer from cell-to-cell within the material. Nutrients do not pass through the hydrogel material with the same level of efficacy as water. Without the proper transfer of nutrients, tissue in the outer portion of the cornea will die causing further deterioration in a patient's eyesight.
Thus, there is believed to be a demonstrated need for a material for corneal implants that will allow for the efficacious transmission of nutrients from the inner surface of a corneal implant to the outer surface, so that tissue in the outer portion of the cornea is properly nourished. There is also a need for a more effective corneal implant for solving the problems discussed above.